1. Field of the Invention
The present invention relates to an ink-jet print head. More particularly, the present invention relates to a protective layer formed for protecting a heating layer of a thermal transfer ink-jet print head and a method of making a print head provided with such a protective layer.
2. Description of the Related Art
In conventional print head applications, two ink ejection techniques have been widely employed in ink-jet print heads. A first technique is to eject ink using a piezoelectric element, and the second technique is to eject ink using ink bubbles produced when instantaneously heating the ink with a heating element. The latter technique is commonly called a thermal transfer technique. Recently, ink-jet print heads of the thermal transfer type have been more commonly used because they can be more easily fabricated in a compact size.
FIG. 1 shows a partial cross-sectional view of the construction of an example conventional ink-jet print head of the thermal transfer type.
Referring to FIG. 1, a conventional ink-jet print head 100 comprises a heating layer 140, an electric conductive layer 150, and a protective layer 160, which are all laminated on a main substrate 120 in the order shown. The heating layer 140 is formed to instantaneously heat ink charged within an ink chamber 110 as described above, and the electric conductive layer 150 is formed for applying electric power to the heating layer 140.
The protective layer 160 is formed for protecting the heating layer 140. In this regard, the conventional protective layer 160 can comprise an insulation layer 164 which is formed over the heating layer 140 and the electric conductive layer 150, and a cavitation layer 161 which is formed on the top surface of the insulation layer 164, as disclosed in U.S. Pat. No. 4,335,389 of Yoshiaki Shirato et al., entitled “Liquid Droplet Ejecting Recording Head”, the entire contents of which are incorporated herein by reference.
The cavitation layer 161 serves to prevent the heating layer 140 from being fractured by a cavitation force produced when ink bubbles (not shown) collapse within the ink chamber 110 after ink droplets are ejected through a nozzle 185. To achieve this function, the conventional cavitation layer 161 can be formed by depositing tantalum (Ta) on the top surface of the insulation layer 164.
In order to protect the heating layer 140 from a cavitation force as described above, a cavitation layer 161 should be wholly superior to remaining layers not only in mechanical properties, such as hardness and elasticity, but also in chemical properties, such as oxidation resistance, for preventing the layer from being readily oxidized by ink charged within an ink chamber 110. However, it is difficult to find such a material that is wholly superior in the aforementioned properties and in particular, it is even more difficult to find such a material that is wholly superior in these properties when incorporated in a thin film layer state in a product.
As an example, a conventional cavitation layer 161 comprised of tantalum (Ta) as mentioned above, is superior in elasticity. However, it is not so superior in hardness and oxidation resistance that it can protect a heating layer 140 for a long period. As a result, if a conventional ink-jet print head 100 is repeatedly used for a long period, the projective layer 160 will be fractured, either by cavitation forces as mentioned above, or by oxidization due to chemical reactions with ink charged within the ink chamber 110. Therefore, a problem arises in that it can become impossible to prevent the heating layer 140 from being damaged. In particular, as ink-jet printers for high-speed printing are being vigorously developed, there is problem in that the replacement period of an ink-jet print head 100 has become shorter and shorter due to the fracture of the heating layer 140 as described above.
Accordingly, a need exists for a system and method to provide an ink-jet print head which can be repeatedly used for a long period with minimal damage to the projective layer by forces such as cavitation and oxidization.